extstore: check malloc in compaction thread.
extstore: check malloc in compaction thread.

simple change.

dormando/memcached,memcached/memcached,dormando/memcached,memcached/memcached,memcached/memcached,gencer/memcached,dormando/memcached,memcached/memcached,gencer/memcached,gencer/memcached,dormando/memcached,dormando/memcached,memcached/memcached,gencer/memcached,gencer/memcached